Application Brief
Induction Heating Applications
Induction heating uses alternating current in driver coils to induce currents in an object and
create heat through precise placement and transient excitation pattern. The thermal and
electrical properties are locally functions of temperature, creating a transient electrothermal
response. Induction heating is used in heat treatment of materials, seals, and joints and in
many other applications.
Keywords
Induced currents, induction heating, eddy currents, Joule losses
Products Used
ANSYS® Maxwell® 15.0, ANSYS Workbench™, ANSYS thermal products
Description
Whether desired or undesired, currents flowing in solid conductors create
Joule losses that contribute heat to a thermal system. Concurrently, the
electrical and thermal properties of materials often are temperature
dependent, which affects current distribution and heat flow. These loss and
temperature variations can be monitored and controlled through proper
engineering and simulated within ANSYS software.
Typical induction heating applications involve a drive coil with high
currents at some kilohertz (kHz) frequency and a conductive target object
placed inside or near the drive coil to induce currents and create heat
(Figure 1). For high-power induction heaters, the drive coils are hollow
with liquid cooling. Additional thermal/structural parts are used to support
the heated object and to properly direct heat flow and duration. The target
object takes the form of either the object of desired temperature increase
or a plate on which the heat-treated object sits (such as with a hot plate or
induction cooking).
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Induction Heating Applications
Figure 1. (left to right) Full 3-D, axisymmetric, and 1/12 wedge
models for simple induction heating example with hollow, liquidcooled drive coil and a conducting target that experiences eddy
currents and Joule heating. This is an overly simplified model in
which the target is thermally insulated except for convective heat
transfer on all outer surface.
a.
b.
a.
c.
d.
Figure 2. Temperature-dependent data for target object that
experiences heating: a) electrical conductivity/resistivity, b)
relative permeability, c) specific heat, and d) thermal conductivity.
Such temperature dependencies make this a very complicated
nonlinear analysis, which is easily accomplished through
simulation.
The kHz region of frequencies is a very interesting simulation space. The
kHz electrical time scale is measured in fractions of a millisecond, while
the signal amplitude is often varied in thermal and structural responses
with time scales that are measured in seconds and greater. You can easily
separate the electrical and thermal simulations, enabling use of a highaccuracy AC simulation of the electromagnetic system with updated
temperatures from the transient thermal simulation. This produces an
efficient and accurate electrothermal response for this class of problems.
The ANSYS Maxwell eddy current solver is used for the AC simulation in
the kHz region to resolve skin depths within objects. The electromagnetic
properties in Maxwell can be defined as a function of temperature (Figure
2), for which the temperature can be defined either per object in Maxwell or
mapped directly from ANSYS thermal tools. Maxwell’s automatic adaptive
meshing allows efficient and accurate solution of losses due to induced
currents for arbitrary geometries. The automated mesh process assures
that the loss calculation is accurate for arbitrary geometry changes; it
robustly captures the skin depth of induced currents, which would not be
possible with manual mesh generation.
The ANSYS thermal solver is used for either static or transient thermal
analysis. The average AC losses from Maxwell are mapped as a spatially
distributed load directly to either the static or transient thermal solver. The
thermal simulation provides a solution to the nonlinear heat flow response
based off the Joule heat losses and any additional loads and boundary
conditions. The transient electrothermal simulation is accomplished with
great flexibility through robust scripting within the ANSYS Workbench
framework, allowing time varying inputs and boundary conditions.
Example results are provided in Figures 3 and 4.
Working within Workbench allows coupling of solution data from the
respective high-fidelity simulations, but it also defines a simplified
workflow and expanded capabilities. The two simulation tools are linked
within Workbench by definition of the project schematic (Figure 5), and the
geometry and solutions are transferred through this link. The geometry is
shared in such a way that only the necessary pieces are used in either the
electromagnetic or thermal simulations, but all the geometry is transferred,
available, and updated whenever geometry changes are applied. This
allows easy geometry variation and design changes; it also makes available
the geometry handling capabilities of ANSYS tools. Further, a structural
simulation can be connected directly to the thermal simulation for
thermally induced stress analysis and fatigue due to thermal cycling.
Figure 3. Transient input and output data for combined
electrothermal simulation. Upper plot shows transient rms
amplitude of input current through AC drive coil, which has
been tapered to keep temperature constant in transient profile;
lower plot provides transient results of minimum and maximum
temperatures on target object.
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Induction Heating Applications
Conclusion
ANSYS provides accurate, flexible, and robust solutions for electromagnetic
and thermal simulations, brought together within the ANSYS Workbench
framework.
Authors
Paul Larsen, paul.larsen@ansys.com
Tomoya Horiuchi, tomoya.horiuchi@ansys.com
Figure 4. Finite element simulations for AC electromagnetics
and transient thermal response produce distributed losses and
temperatures – data that is shared between the two simulation
tools. The distributed electromagnetic loss calculated in Maxwell
is transferred as an imported load to ANSYS thermal tools, which
calculate the temperature and map the distributed temperature
data back to Maxwell. The visualizations allow rapid identification
of heat flow paths and local hot spots.
Figure 5. ANSYS Workbench enables transfer of geometry
and solution data. This allows mapping of losses from an
electromagnetic simulation to a static and/or transient thermal
simulation along with feedback mapping of temperature for
electromagnetic properties.
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